1. Field of the Invention
The present invention relates to a battery pack and a charge circuit for the battery pack, more particularly to a battery pack for supplying electric energy to a portable terminal device and a charge circuit for the battery pack.
2. Description of the Related Art
A portable terminal device such as a cellular phone, a PDA (Personal Data Assistant), and a notebook PC (Personal Computer) uses a rechargeable battery, for example, a lithium-ion secondary battery. Such battery packs release the devices from being wired, that is performances are available even if the device is outdoors where an outlet is unavailable.
Since such the battery packs are rechargeable by a charge circuit with, for example, an AC adapter which interconnects an outlet and the battery pack, the performance of the device is sustainable by recharging the battery pack.
However, long-time use of the device outdoors exhausts the battery pack, and the exhausted battery pack no longer activates the device until it recharged. Since recharging is the user""s task, battery storage may occur if the user forgets recharging.
Unexamined Japanese Patent application KOKAI Publication No. H8-107581 discloses a technique for solving the above problems. This reference discloses a wireless telephony device comprising a solar panel which charges a secondary battery for activating the device.
The solar panel disclosed in Unexamined Japanese Patent Application KOKAI Publication No. H8-107581 is designed for supplying energy only to a liquid crystal display panel. If electric energy supplied by the solar panel is larger than electric energy necessary for driving the display panel, it has surplus energy which is unused. That is, energy sufficiency is not good. Especially, in case of a wireless telephone which requires less electric energy (less power consumption) for driving its liquid crystal panel, more surplus energy is unused.
The technique disclosed in Unexamined Japanese Patent Application KOKAI Publication No. H8-107581 is suitable for a device such as a wireless telephone whose display (LCD) is not required to be seen while the device is used. That is, it is not suitable, for example, for a notebook PC whose LCD panel (display) is required to be seen while the device is used.
In a case where a device has been unused for a long time, a user generally uninstalls a battery pack from the device to store it. In this case, if the detached battery has a residual energy, the battery pack will lose its capacity performance.
The present invention has been made in consideration of the above, it is an object of the present invention to provide a battery pack and a charge circuit therefor which use electric energy from a solar panel efficiently, thus extending life of battery installed in an equipment (portable terminal device) for longer usage.
It is another object of the present invention to provide a battery pack and a charge circuit therefor which are helpful for storing uninstalled battery pack for a long time with reducing deterioration of capacity performance of the battery.
To achieve the above described objects, a battery pack according to a first aspect of the present invention is a battery pack for supplying electric energy to a portable terminal device, comprises:
a solar panel unit which converts light energy into electric energy;
a battery which is rechargeable with the electric energy;
an interface between the battery pack and the portable terminal device which supplies the electric energy to the portable terminal device;
an energy supplier being connected to the solar panel unit, the battery and the interface, which supplies the electric energy from the solar panel unit to the interface when the portable terminal device is in operation, while supplying the electric energy from the battery to the interface or charging the battery with part of the electric energy from the solar panel unit in accordance with the amount of electric energy to be used by the portable terminal device.
According to the above structure, the solar panel unit converts light energy into electric energy, and supplies it to the energy supplier. When the portable terminal device is resting, the battery is charged with the electric energy supplied to the energy supplier. Accordingly, the battery is automatically charged with the electric energy from the solar panel unit. As a result, battery life extends, thus the portable terminal device can be used for a longer time. When the portable terminal device is in operation, the electric energy from the solar panel unit is supplied to the portable terminal device, at the same time the portable terminal device uses the electric energy charged in the battery as additional energy or the battery is charged, in accordance with the amount of electric energy to be used by the portable terminal device. As a result, the electric energy from the solar panel unit is used efficiently.
The solar panel may comprise: solar cells; and an external power supply interface which supplies the electric energy generated by the solar cells to the energy supplier.
The external power supply interface may accept connection with an AC adapter which obtains commercial electric energy.
The energy supplier may supply the electric energy from the AC adapter when the portable terminal device is in operation, while supplying the electric energy from the battery to the interface or charging the battery with part of the electric energy from the AC adapter in accordance with the amount of electric energy to be used by the portable terminal device. In this case, the electric energy from the AC adapter is supplied to the portable terminal device, at the same time, the portable terminal device uses the electric energy charged in the battery as additional energy or the battery is charged, in accordance with the amount of electric energy to be used by the portable terminal device.
The battery pack may further comprise a regulator between the solar cells and the external power supply interface. If the voltage regulated by the regulator is set to a voltage higher than the voltage supplied by the AC adapter, priority is given to the electric energy from the solar panel unit, thus, the electric energy from the solar panel unit is used efficiently.
The battery pack may further comprise a discharge circuit which arbitrarily discharge residual energy in the battery. This structure is helpful for restricting deterioration of capacity performance of the battery.
The energy supplier may comprise:
a variable resistance element which transmits the electric energy supplied from the solar panel unit to the interface; and
a controller circuit which controls residence of the variable resistance element,
the controller circuit controls the residence of the variable resistance element so that the battery is charged with a constant charge current. According to this structure, the battery is charged with the electric energy from the solar panel unit.
The variable resistance element may comprise a MOSFET whose one end of a current path is connected to the external power supply interface via an anti-reverse circuit, the other end of the current path is connected to the interface, and a gate is connected to the controller circuit,
The controller circuit may control a voltage to be applied to the gate of the MOSFET so that a constant electric current flows in the battery while the battery is being charged. According to this structure, the battery is charged with a constant charge current.
The controller circuit may be activated by the electric energy supplied from the external power supply interface.
The battery may be substantially connected to a resistance element in series.
The controller circuit may measure voltage drop at the resistance element, and may control a voltage to be applied to the gate of the MOSFET so as to regulate the voltage drop to be constant.
A charge circuit according to a second aspect of the present invention is a circuit for charging a battery for a portable terminal device, comprises:
a controller which controls electric energy from a solar panel unit;
a transistor which is activated and inactivated under a control of the controller; and
a current detector resistance element which detects electric current flowing through the battery,
wherein the controller activates the transistor to supply electric currents to the battery and the current detector resistance element, and controls the transistor to be activated or inactivated so that a voltage between both ends of the current detector resistance element is regulated, thus the battery is charged with the electric energy supplied to the controller, while the portable terminal device is resting, and
the controller activates the transistor to supply the electric energy from the solar panel unit to the portable terminal device, and supplies the electric energy from the battery to the portable terminal device or charges the battery with part of the electric energy from the solar panel unit, in accordance with the amount of electric energy to be used by the portable terminal device, while the portable terminal device is in operation.
According to this structure, the battery is charged with the electric energy from the solar panel while the portable terminal device is resting, thus, the portable terminal device can be used for a longer time. When the portable terminal device is in operation, the electric energy from the solar panel is supplied to the portable terminal device, at the same time, the portable terminal device uses the electric energy charged in the battery as additional energy or the battery is charged, in accordance with the amount of electric energy to be used by the portable terminal device. As a result, the electric energy from the solar panel is used efficiently.
The transistor may be connected to an interface which accepts an external power source, an anode of the battery, and the controller, and
one end of the current detector resistance element may be connected to a cathode of the battery and the controller, and the other end of the current detector resistance element is grounded.